1. Field of the Invention
The invention relates to a proximity switch having a magnetic field-sensitive sensor.
Conventional mechanical switches are increasingly being displaced, in particular in motor vehicle applications, by non-contacting proximity switches having a magnetic field-sensitive sensor, for example a Hall sensor or a magneto resistor. In principle, Hall sensors are composed of a semiconductor layer, in particular one made of silicon, which is supplied with a constant current. The constant current is influenced by a magnetic field component at right angles to the layer and the sensor supplies a Hall voltage which may be evaluated and which is proportional to the applied magnetic field strength. At present, Hall sensors are expediently used in the form of an integrated circuit which already contains an evaluation circuit which is suitable for evaluating the switching state.
2. Description of the Prior Art
German Offenlegungschrift 39 01 678 discloses positioning the magnetic field-sensitive sensor in a magnetic field-free zone of a special permanent magnet arrangement. In order to achieve a high temperature stability, the permanent magnet in the known proximity switch is therefore configured in such a way that an annular pole surface results. In this case, driving by a flat ferromagnetic triggering part is carried out at right angles to the pole plane, the magnetic field-free zone not being canceled when the triggering part is brought close but only when moving away from the sensor.